I do not understand the current trend of legacies UADL etc expanding destinations while they are sinking into Chp 11. Also US announced more destinations and they are sinking just as fast. Please explain?

It's not really expansion. DL just de-hubbed DFW and US also de-hubbed PIT. This means cancelling hundreds of daily flights systemwide, the airplanes can't be grounded. All that they are doing is shifting their operations to other cities where there is a larger possibility of profit with their existing fleets to make up for the de-hubbed areas.